In Japan, the first cause of death is cancer, and cancer is steadily increasing. In recent Japan in which improvement in quality of life (QOL) is needed, therapy using radiation attracts attention as a cancer therapy method. In order to improve the QOL as the need, a radiation cancer therapy technique which is a seed becomes highly accurate, and radiation cancer therapy also starts to be widespread in Japan.
Radiation used for therapy includes an X-ray, a particle beam (a proton beam or a heavy particle beam), an electron beam, and a neutron beam. Particularly, in recent years, a particle beam therapy apparatus using a proton beam and a heavy particle beam therapy apparatus using a heavy particle beam (for example, a carbon beam) have been remarkably developed. A patient is irradiated with a particle beam by using the property that the proton beam and the heavy particle beam generate a dose peak (black peak) by being intensively applied with energy immediately after being stopped, and thus a dose can be applied to an affected part of cancer in a concentration manner, so that low invasive and highly accurate cancer therapy can be expected.
Also in cancer therapy using an X-ray, intensity-modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT) have been developed, and an effort to cause a dose in X-ray irradiation to concentrate on an affected part of cancer has been made. In accordance with sophistication of a radiation therapy apparatus, there is the need for improvement of the whole accuracy related to radiation therapy, such as the accuracy of a therapy plan and the accuracy of patient positioning, dose rate measurement for quality assurance (QA) of a therapy plan and a therapy apparatus.
In radiation therapy, a total amount of damage received by an affected part is evaluated on the basis of a total amount of (absorbed dose) energy applied to the affected part of cancer due to radiation, and a therapy plan for a patient is made on the basis of the evaluation. In the radiation therapy, a dose rate is measured in order to obtain the absorbed dose. In the radiation therapy, an ionization chamber of which stability and reproducibility are favorable are widely used to measure a dose rate of radiation applied to a patient. However, the ionization chamber has a limit in miniaturization due to a detection principle thereof, and, instead thereof, a dose distribution measurement using a semiconductor detector which is relatively easily miniaturized is performed. In a case where even a signal processing system is included, the semiconductor detector also has a limit in miniaturization. Since a high voltage is required to be applied in such a radiation detector, it is difficult to insert the radiation detector into a patient's body, and to measure a dose rate. Such a detector generally has high density, has a greater interaction with radiation than a substance in the body and water, and thus the influence of the radiation detector cannot be disregarded.
As described above, in a situation in which an actual internal absorbed dose cannot be understood, a dose distribution of an affected part obtained through therapy planning has a margin by taking into consideration body motion of the patient due to respiration or the like. This is a cause of reducing the irradiation accuracy of radiation to an affected part. In the body of a patient, in a case where a normal part sensitive to radiation is present near an affected part which is a therapy target part, radiation therapy of the affected part is difficult.
Therefore, a method of predicting an internal absorbed dose by using a radiation detector disposed outside the body of a patient is effective, and there are the following prediction techniques.
A radiation therapy apparatus disclosed in JP-A-2003-210596 is an electron beam therapy apparatus, and irradiates an affected part of a patient with an electron beam. An electron gun and a linear accelerator are provided in a rotated gantry, and an electron beam generated from the electron gun is accelerated in the linear accelerator, and is then applied to an affected part of a patient on a bed from an irradiation head. The electron beam applied to the affected part and transmitted through the patient is detected by a radiation detector which is disposed at a lower part of the bed directly under the affected part. A dose applied to the affected part is obtained on the basis of a radiation detection signal output from the radiation detector.
In the radiation therapy apparatus disclosed in JP-A-2003-210596 (US2003/0095625A1), radiation transmitted through the patient is detected by a radiation detector disposed outside the body of the patient irradiated with the radiation, and thus there is a possibility that an accurate internal absorbed dose cannot be measured. Temporal changes of a position of an organ (affected part) in the body and a size of the organ in a radiation irradiation direction between the time of therapy planning and the time of therapy execution on the affected part using irradiation with radiation, and patient positioning during therapy also cause errors. An internal dose distribution of the patient is estimated through calculation using a dose which is obtained on the basis of a radiation detection signal output from the radiation detector outside the body. A calculation error in this estimation cannot be disregarded.
In order to reduce such errors, a radiation detector is preferably inserted into the body. A radiation detector inserted into the body is disclosed in JP-A-2001-56381. The radiation detector has a scintillation fiber, and an optical fiber is connected to the scintillation fiber via a band-pass filter. JP-A-2001-56381 discloses a technique in which the scintillation fiber and the optical transmission fiber are inserted into the body, and thus contribution of Cherenkov light which is noise can be removed such that a true radiation dose can be measured.
“Bragg Curve Measurement in Near-Infrared Single Photon Counting Mode”, Katsunori UENO and others, the 110th Japanese Society of Health and Medical Sociology, Vol. 35, Supplement No. 3 (September, 2015), page 77 discloses an optical fiber type online dosimeter (internal dosimeter) which can measure an irradiation dose applied to a patient during proton therapy. The optical fiber type online dosimeter uses Nd:YAG for a detection unit, and performs single-photon counting on near-infrared light generated by Nd:YAG.
“Current status and vision of study for severe accident instrumentation system, 1. Optical fiber-type radiation monitor system”, Takahiro TADOKORO and others, 2015 Annual Meeting of the Atomic Energy Society of Japan Proceedings, Lecture No. 117, issued on Mar. 5, 2015, discloses an optical fiber type radiation monitor, applied to a nuclear power plant, is configured with a detection unit, an optical fiber unit, and an optical measurement unit using Nd:YAG. The optical fiber type radiation monitor can measure a dose rate with the accuracy equal to or lower than ±4% FS in a range of a dose rate of 1.0×10−2 to 9.54×104 Gy/h.
In an X-ray therapy apparatus, an energy spectrum of an X-ray has a very wide distribution according to an X-ray generation principle that an accelerated electron collides with a target such as tungsten, and an X-ray is generated due to braking radiation occurring at that time. JP-A-2015-204985 (US2015/0301202A1) discloses an X-ray energy spectrum measurement method which is an example of a method of measuring an energy spectrum. In the X-ray energy spectrum measurement method, X-rays are applied to respective portions of which thicknesses are different from each other by using an attenuation member of which a thickness changes stepwise, and energy of each X-ray transmitted through each portion is obtained by using the Bayesian inference formula. Energy of a signal output from a radiation detector which detects an X-ray transmitted through a subject is corrected by using the obtained energy of an X-ray.
In a radiation detection system disclosed in JP-A-2007-114067, a scintillator layer is formed on an inner surface of each of two optical fibers which are disposed in parallel and to which X-rays are incident, and an X-ray transmitted through one optical fiber is incident to the other optical fiber. Information regarding a radiation flying direction is generated on the basis of a signal output from the scintillator layer of each optical fiber. The information regarding a flying direction is created on the basis of, for example, a calculated incidence time point, the incidence time point at which radiation is incident to each optical fiber being calculated on the basis of an output signal from each scintillator layer.
JP-A-11-160437 discloses an optical fiber type radiation detector. In the optical fiber type radiation detector, a plurality of (for example, seven) optical fibers are inserted into a scintillator. Light generated in the scintillator when radiation is incident to the scintillator is transmitted to a counter through the optical fibers, and the number of pulses is counted by a counter.
An endoscope system disclosed in JP-A-2009-189653 (US2009/0209812A1) includes a rotary self-propelled endoscope, a first control device, a second control device, and an aspirator. The rotary self-propelled endoscope has an insertion section and an operation section. The insertion section has in an order from the distal end thereof: an insertion section main body having a distal end portion and a bending portion; an insertion assistance device; an insertion section receiving case; a distal end side guide tube which is a corrugated tube interposed between the insertion assistance device and the insertion section receiving case; an external drive section (second drive section) which is provided on an outer surface of the distal end side guide tube; a coupling section which is provided in the insertion section receiving case; and an operation section side guide tube which is a corrugated tube interposed between the operation section and the coupling section. The operation section has a motor unit (first drive section), a grasping section, and a main operation section which is an operation instruction section.
The insertion section main body configuring the insertion section has an outer shaft and an inner shaft rotatably inserted into the outer shaft. The outer shaft (driving force generation portion) is provided with a coil which is wound not densely and is biocompatible, and a resin thin film, which links between the striae of the coil, is biocompatible and covers the coil. The inner shaft is rotatably inserted into the outer shaft, and is configured to allow the distal end portion of the insertion section main body to rotate with good following capability by reducing torsion of the insertion section main body. In order to obtain anti-torsion property, the inner shaft includes a first coil which is wound not densely in the normal direction and is biocompatible, a second coil which is wound not densely in the direction opposite to that of the first coil to be disposed between the striae of the first coil and which is biocompatible, a third coil which is wound not densely in the opposite direction (normal direction) to that of the second coil, to be disposed between the striae and on the outer periphery of the second coil and which is biocompatible, and a resin thin film which links between the striae of the third coil, covers the third coil, and is biocompatible.
Each distal end of the outer shaft and the inner shaft is fixed to a distal end supporting section which is rotatably connected to the insertion section main body including the distal end portion and bending portion, via adhesive joints. An imaging unit is provided at the distal end portion, and a cable tube having a cable built thereinto which is connected to the imaging unit is provided inside the inner shaft.
The first control device is connected to a footswitch, via a cable, which enables an operation to start or stop the rotations of the outer shaft which is a rotary cylindrical body and the inner shaft which is a torque transmission member. The second control device is connected to the aspirator.
The outer shaft is rotated by an external drive section. The external drive section includes a first roller, a second roller, a third roller, and a first motor connected to the first roller. The first roller, the second roller, and the third roller are disposed to be inclined such that the circumferential direction of each periphery surface is generally along the direction of the helical configuration formed on the surface of the outer shaft. The first roller is rotated due to driving of the first motor, and thus the outer shaft is rotated. The inner shaft is rotated due to driving a second motor included in the motor unit. When a rotation control command is output from the first control device by operating the footswitch, the first motor and the second motor are rotated, and when a stop control command is output from the first control device, the first motor and the second motor are stopped. JP-A-2009-189653 is referred to with respect to detailed configurations and operations of the endoscope system.